Studies of intracardiac receptors whose afferent nerve fibers traverse the sympathetic nerve tracts indicate that there is a quantitative positive relationship between afferent nerve discharge frequency and peak developed left ventricular pressure for receptor located within the left ventricle and a similar relationship between nerve activity and peak developed right ventricular pressure for receptor located within the right ventricle. Sympathetic afferent nerve tracts were also found to carry information from inflation-type intrapulmonary receptors. The afferent nerve activity in these nerve fibers was quantitatively related to the lung inflation volume and to airway pressure during lung inflation. These cardiopulmonary afferent fibers play a role in the regulation of the heart and in the regulation of breathing frequency. Central electrical stimulation of cardiopulmonary afferents which traverse sympathetic nerve tracts produced inhibition of inspiration. In other studies, stimulation of cardiopulmonary sympathetic afferent nerves resulted in an increase in left and right ventricular pressure and central aortic blood flow. BIBLIOGRAPHIC REFERENCES: Kostreva, D.R., E.J. Zuperku, G.L. Hess, R.L. Coon and J.P. Kampine. Pulmonary afferent activity recorded from sympathetic nerves. J. Appl. Physiol., 39: 37-40, 1975. Kostreva, D.R., G.L. Hess, E.J. Zuperku, J. Neumark, R.L. Coon and J.P. Kampine. Cardiac responses to stimulation of thoracic afferents in the primate and canine. Am. J. Physiol., 1976.